The hpsa firmware will bypass the cache for any request larger than 1MB,
so we should cap the request size to avoid any performance degradation
in kernels later than v4.3

This degradation is caused from d2be537c,
which changed max_sectors_kb to 1280k, but the hardware is able to work
fine with it, so the true fix should be from hpsa driver.
Signed-off-by: Yadan Fan <ydfan@suse.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Acked-by: Don Brace <don.brace@microsemi.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>